1. FIELD OF THE INVENTION
The present invention relates generally to optical projection lithography methods and photolithography photomasks, and particularly to optical photolithography mask blanks for use in optical photolithography systems utilizing deep ultraviolet light (DUV) wavelengths below 300 nm, such as DUV projection lithography systems utilizing wavelengths in the 248 nm region and the 193 nm region.
2. TECHNICAL BACKGROUND
Projection optical photolithography methods/systems that utilize the deep ultraviolet wavelengths of light below 300 nm provide benefits in terms of achieving smaller feature dimensions. Such methods/systems that utilize deep ultraviolet wavelengths in the 248 nm and the 193 nm wavelength regions have the potential of improving the manufacturing of integrated circuits with smaller feature sizes but the commercial use and adoption of deep UV in high volume mass production of integrated circuits has been slow. Part of the slow progression to DUV by the semiconductor industry has been due to the lack of economically manufacturable photomask blanks with high quality optical performance. For the benefit of deep ultraviolet photolithography in the 248 nm region such as the emission spectrum DUV window of a KrF excimer lasers and the 193 nm region such as the ArF excimer laser emission spectrum to be utilized in the manufacturing of integrated circuits there is a need for mask blanks that have beneficial optical properties and chemical durability that can be manufactured economically and utilized in photomasks.
Photomask blanks used in such lithography methods/systems are different from the other optical elements of the system such as lenses and mirrors in that the photomasks are generally very thin and play a unique part in the system in terms of providing a substrate for integrated circuit patterns that are projected through the system. Patterns of the integrated circuits to be made are formed on the photomask blanks, so that an image of the pattern on the photomask blank can be projected through the lithography system and printed on a surface of an integrated circuit semiconductor wafer. Photomask blanks must meet very strict requirements for dimensional stability to avoid warping and shrinking and for optical properties such as high transmission in order to ensure the extreme accuracy required to form very fine integrated circuit patterns and inhibit the distortion there of.
The present invention overcomes problems in the prior art and provides a means for economically manufacturing high quality improved photomask blanks and high performance masks that can be used to improve the manufacturing of integrated circuits with deep ultraviolet wavelengths.